The Classified Code-Breakers of World War II

A woman adjusting a large machine
Woman working on a code-breaking machine

Background of Cryptanalysis

Cryptography is the art of protecting information using codes and ciphers, and it has been used for thousands of years. In ancient times all the way until about World War I, it has been done on paper or with very simple machines, and then became more and more complex with the advance of technology. Modern codes are generally done with computers in a way that no human mind could break without technology. The Zimmeran telegram led to the U.S. entering World War I. Allies cracking Nazi codes may have shorted World War II by as much as two years.

A stone wall with a painting of an Egyptian man
The tomb of Khnumhotep II
A transcript of the Zimmerman telegraph
The cracked Zimmerman telegram

World War II

In World War II, traditional paper codes were used at the same time machine-made codes were really hitting their stride. Some of these code developments have only hit public knowledge in the 1990s and early 2000s.

A woman in a trenchcoat and hat
Elizebeth Friedman

Elizebeth Friedman

Elizebeth Friedman, Elizebeth spelled with three ees instead of an a, has been often called “America’s first female crytanalyst”. She was born to a Quaker family on a farm in Huntington, Indiana. She was the youngest of ten children, and graduated from Hillsdale College in Michigan with a degree in English literature, and experience in Latin, Greek, and German in 1915. She served as a substitute principal for a high school for several months and then moved back in with her parents. In 1916, she visited Newberry Library in Chicago looking for work, and spoke to the librarian.

A smiling older couple stare off camera, laughing
The Friedmans

Uncle Sam’s Code-Breakers

The SIS team (Frank Rowlett far right, William Friedman center)

The Allies Link Up

The United States code-breaking team, the Signal Intelligence Service broke the highest level Japanese code system, nicknamed Purple, before World War II even started. Purple had replaced another Japanese machine called M-1 Orange, which was broken by U.S. Navy code-cracker Agnes Driscoll, who also went by the fantastic nickname Madame X. The U.S. won the Battle of Midway at least partially because they had cracked Japanese code system JN-25, which the Japanese did not notice and continued using.

Women sitting at desks working on small machines
Female code-breakers at Arlington Hall

Venona and the Rosenbergs

The U.S. ran the Venona Project during World War II and continued through the Cold War into 1980 to decrypt Soviet communications. The project decrypted about 3,000 messages. They discovered the Cambridge 5 espionage ring that operated in the U.K. from the 1930s to the 1950s, and also Soviet spying on the Manhattan Project, the building of the nuclear bomb, which is discussed in Episode 1 of this podcast. The Soviets were using one-time pads, which as mentioned, when used correctly are uncrackable. The problem was that the Soviets accidentally reused entire pages of code in multiple one-time pad booklets, which allowed them to be cracked by American cryptanalysts. Most of these codes-crackers were young women.

Ethel and Julius Rosenberg sitting on either side of a chain link fence
Ethel and Julius Rosenberg


An wooden book containing metal keys and plugs
An Enigma machine
The Polish Enigma team

A head of the project said that the Enigma code-cracking “would never have gotten off the ground if we had not learned from the Poles, in the nick of time, the details both of the German military version of the commercial Enigma machine and of the operating procedures that were in use.”

After the Enigma was broken, the Germans developed Schlusselgerat 41 to replace it, but it wasn’t widely used. When the war ended, the British intelligence officers were told not to reveal that the Enigma had been broken, as they were worried the defeated Nazis would say that they had been beaten unfairly.

A young Alan Turing in a black and white photo
Alan Turing

Alan Turing

Alan Turing is one of the most famous code-crackers to ever live. He was born in London in 1912, and his middle name literally had the word Math in it, Mathison. His father was on leave from the Indian Civil Service, and his mother was from an English-Irish noble family. He had one older brother, John, and his parents would often travel to India for his father’s work, so the children would stay with family friends.

Alan Turing and Christopher Morcom (Photo credit Polari Magazine)

“I am sure I could not have found anywhere another companion so brilliant and yet so charming and unconceived. I regarded my interest in my work, and in such things as astronomy (to which he introduced me) as something to be shared with him and I think he felt a little the same about me … I know I must put as much energy if not as much interest into my work as if he were alive, because that is what he would like me to do.”

Turing continued to write her for many years. Although Turing has been known as an atheist, he wrote to Marcom’s mother at one point,

Alan Turing running in front of a crowd, wearing a paper racing number 140
Turing running

“ACTION THIS DAY. Make sure they have all they want on extreme priority and report to me that this has been done.”

Two hundred bombe devices were eventually made.

An old book with the title “Criminal Law Amendment”
British gross indecency laws were contained in this book

“Thousands of people have come together to demand justice for Alan Turing and recognition of the appalling way he was treated. While Turing was dealt with under the law of the time and we can’t put the clock back, his treatment was of course utterly unfair and I am pleased to have the chance to say how deeply sorry I and we all are for what happened to him … So on behalf of the British government, and all those who live freely thanks to Alan’s work I am very proud to say: we’re sorry, you deserved so much better.”

Another petition was started to have Turing formally pardoned. It was originally rejected because homosexuality was illegal at the time he comitted the so-called crime. But politician John Leech continued pushing for the pardon for years. Famous scientists including Stephen Hawking threw their support behind the push. In an unprecedented move, Queen Elizabeth pardoned Alan Turing in 2014.

“The fact remains that everyone who taps at a keyboard, opening a spreadsheet or a word-processing program, is working on an incarnation of a Turing machine.”

A statue of Alan Turing sitting on a bench surrounded by bouquets of flowers
Alan Turing’s statue

“We can only see a short distance ahead. But we can see plenty there that needs to be done.”

Another statue of Alan Turing working at a desk
Statue of Alan Turing (Photo credit BBC)




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